Method and device for forming required gas atmosphere

ABSTRACT

The present invention provides an apparatus and a method for forming a desired gas atmosphere in an inner space of a casing.  
     This apparatus comprises a casing ( 1 ) having a gas introduction opening ( 3 ) for introducing a gas into the casing and a gas discharge opening ( 5 ) for discharging the gas from the casing, a gas circulating tube passage ( 8 ) communicated with the casing for effecting circulation of the gas, a circulating fan ( 11 ) for effecting circulation of the gas in the casing through the gas circulating tube passage and a valve ( 6, 7 ) switchable between a position for conducting the introducing and discharging of the gas into and from the casing through the gas introduction opening and the gas discharge opening and a position for effecting circulation of the gas in the casing through the gas circulating tube passage. The apparatus further comprises a trap ( 10 ), a filter ( 4 ) and a heat exchanger ( 9 ) for conducting a desired treatment with respect to the circulated gas, such as removal of particles.  
     In this apparatus, the introducing of gas into the casing and the discharging of gas from the casing are conducted at the same time, to thereby remove air which exits in the casing before operation and fill the casing with the introduced gas. When the casing is filled with the introduced gas, the introducing and discharging of the gas is stopped and the gas is subjected to circulation. The gas atmosphere in the casing is maintained in a predetermined condition.

TECHNICAL BACKGROUND

[0001] The present invention relates to an apparatus and a method forfilling a space surrounded by a housing or casing with an inert gas andforming a desired gas atmosphere in the space.

[0002] For example, in a batch-type low-pressure CVD apparatus, a numberof wafers are placed in a casing and a desired film is formed on asurface of each wafer by chemical vapor deposition. The wafer surfacemust be protected against oxidation due to oxygen or moisture containedin the ambient atmosphere, so as to prevent an oxide film from beingformed on the wafer surface.

[0003] To this end, conventionally, as shown in FIG. 1, a dry inert gasG is introduced through a gas introduction opening 3 into a space 2surrounded by a casing 1, and particles are removed from the gas bymeans of a particle-removing filter (such as an HEPA or ULPA filter) 4,to thereby form a dry, inert gas atmosphere in the space 2 and preventthe above-mentioned oxidation. At the same time, the gas is dischargedfrom the space 2 through a discharge opening 5 at a predetermined flowrate, thus preventing contamination of the gas contained in the space.

[0004] Thus, in such a system as mentioned above, an inert gas is usedin a large amount, so that a running cost becomes inevitably high.

DISCLOSURE OF THE INVENTION

[0005] In view of the above, the present invention has been made. It isan object of the present invention to provide an apparatus and a methodwhich enable an inert gas to fill a space surrounded by a casing andform a desired gas atmosphere in the space, and are capable of reducingthe amount of gas used therein.

[0006] That is, the present invention provides an apparatus for forminga desired gas atmosphere, comprising: a casing having a gas introductionopening for introducing a gas into the casing and a gas dischargeopening for discharging the gas from the casing; a gas circulating tubepassage fluidly communicated with the casing for effecting circulationof the gas; a circulating fan for effecting circulation of the gas inthe casing through the gas circulating tube passage; and a valveswitchable between a position for conducting the introducing anddischarging of the gas into and from the casing through the gasintroduction opening and the gas discharge opening and a position foreffecting circulation of the gas in the casing through the gascirculating tube passage.

[0007] In this apparatus, at an initial stage of operation, a gas isintroduced into the casing through the gas introduction opening whilethe introduced gas is discharged through the gas discharge opening. Thisis continued until air which exists in the casing before operation isdischarged from the casing and the casing is filled with the introducedgas. When the casing is filled with the introduced gas, the valve isswitched so that the gas in the casing is subjected to circulationthrough the gas circulating tube passage. With the gas being circulated,a desired treatment for maintaining the gas in a predeterminedcondition, such as removal of moisture from the gas, can be conducted.

[0008] More specifically, the gas circulating tube passage can beconnected between the gas introduction opening and the gas dischargeopening. The switchable valves can be respectively provided at the gasintroduction opening and the gas discharge opening so that theabove-mentioned switching is conducted.

[0009] In the gas circulating tube passage, a filter for removingparticles contained in the circulated gas and a trap for cooling andcondensing moisture contained in the gas and removing the moisture fromthe gas may be provided. Further, a heat exchanger for effecting heatexchange between the gas which flows into the trap and the gas whichflows out of the trap may also be provided.

[0010] Further, in the casing, a gas flow equalizing mechanism may beprovided in the casing for equalizing flow of the gas passed through thecasing.

[0011] The present invention also provides a method for forming adesired gas atmosphere in a space in a casing. This method comprises thesteps of: introducing a gas into the space while discharging the gasfrom the space; and stopping the introducing and discharging of the gaswhen the space is filled with the gas, and circulating the gas in thespace through a gas circulating passage communicated with the casing.

[0012] This method may further comprise the step of conducting a desiredtreatment with respect to the circulated gas, such as removal ofparticles. The method may further comprise the step of equalizing flowof the gas in the casing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows a conventional apparatus for forming a desired gasatmosphere in a space surrounded by a casing.

[0014]FIG. 2 shows an apparatus of the present invention for forming adesired gas atmosphere.

[0015]FIG. 3 shows an example of a general construction of a trap usedin the apparatus of FIG. 2. FIG. 3(a) is a side cross-sectional view andFIG. 3(b) is a cross-sectional view, taken along the line A-A in FIG.3(a).

PREFERRED EMBODIMENTS OF THE INVENTION

[0016] Hereinbelow, an embodiment of the present invention is described,with reference to the accompanying drawings.

[0017] As shown in FIG. 2, an apparatus of the present inventioncomprises a casing 1 such as that mentioned above and a gas circulatingdevice 20 for circulating a gas through an inner space 2 of the casingand forming a desired gas atmosphere in the inner space.

[0018] As in the case of the above-mentioned conventional apparatus, thecasing 1 has a gas introduction opening 3 and a gas discharge opening 5.In this embodiment, as in the case of a CVD apparatus, the inner space 2of the casing is adapted to have an inert gas atmosphere, such as anitrogen (N₂) gas atmosphere or an argon (Ar) gas atmosphere.

[0019] The gas circulating device has a gas circulating tube passage 8communicated with the gas introduction opening 3 and the gas dischargeopening 5 through switch valves 6 and 7. The switch valves 6 and 7 areswitchable between a position such that the gas is supplied to anddischarged from the inner space 2 of the casing 1 and a position suchthat the supplying and discharging of the gas is stopped and the gas inthe inner space 2 is subjected to circulation through the circulatingtube passage 8.

[0020] A circulating fan 11 is provided at the gas introduction opening3. A filter 4 is provided downstream of the fan 11. Further, a gas flowequalizing mechanism 12 is provided downstream of the filter 4 so as toequalize flow of an inert gas in the space 2.

[0021] A heat exchanger 9 and a trap 10 are provided in the gascirculating tube passage 8. The trap is used for cooling an inert gas GIpassed therethrough so that moisture or an organic gas (organiccontaminate) contained in the gas are condensed and caught thereon forremoval. An inert gas G2 after removal of moisture or an organic gas isreturned to the casing 1 through the filter 4.

[0022] The heat exchanger 9 effects heat exchange between the inert gasG1 which is introduced into the trap 10 and the inert gas G2 which isdischarged through the trap so that the temperature of the inert gas G2returned to the casing is maintained at a level higher than apredetermined temperature.

[0023]FIG. 3 shows an example of a general construction of the trap 10.FIG. 3(a) is a side cross-sectional view and FIG. 3(b) is across-sectional view, taken along the line A-A in FIG. 3(a). As shown inFIG. 3, the trap 10 comprises a cold head 10-1 and a helium compressor10-2. The cold head 10-1 comprises a cylindrical casing 10-1 a and acylindrical condenser 10-1 b which is made of a material having goodheat conductivity (a metallic material) and provided in the casing in acoaxial relation. The cylindrical compressor 10-1 b is connected to thehelium compressor 10-2 through a helium refrigerator 10-1 c, and isadapted to be cooled to, for example, −100° C. to −200° C. by means of ahelium gas. The condenser has a number of radial fins. The inert gas G1which has flowed into the casing 10-1 a of the cold head 10-1 is cooledby the condenser, and moisture or an organic gas contained in the gas G1is condensed and caught on a surface of the condenser.

[0024] As a bearing for the circulating fan 11, it is preferred that amagnetic bearing be used and a magnetic bearing portion and a motorportion be imparted with a canned structure, in order to preventcontamination of the inert gas with particles or organic materials.

[0025] To use the apparatus of the present invention, the switchablevalves 6 and 7 are first brought into a non-circulation position and aninert gas G is introduced through the gas introduction opening 3 intothe casing and discharged from the casing through the gas dischargeopening 5. The introduced gas G is passed through the circulating fan11, the filter 4 and the gas flow equalizing mechanism 12, in which theflow of the gas is equalized and introduced into the space 2.

[0026] When the space 2 is filled with the inert gas G while oxygen andmoisture in the space 2 are removed, the switchable valves 6 and 7 areswitched to a gas circulating position. Consequently, the inert gas inthe space 2 is passed through the switchable valve 7, the heat exchanger9, the trap 10, the heat exchanger 9, the switchable valve 6, thecirculating fan 11, the filter 4 and the gas flow equalizing mechanism12, in which the flow of the gas is equalized and introduced into thespace 2.

INDUSTRIAL APPLICABILITY

[0027] According to the present invention, the amount of gas utilizedcan be reduced to a large extent as compared to the above-mentionedconventional technique. When the apparatus of the present invention isused as, for example, a batch-type low-pressure CVD apparatus, a numberof semiconductor wafers are set in the space 2 of the casing and anitrogen gas or an argon gas is introduced into the space and issubjected to circulation. Consequently, the concentration of oxygen andthe concentration of moisture in the gas in the space 2 can besuppressed to an extremely low level, and oxidation of the semiconductorwafer surfaces can be prevented. The inert gas should be supplementallyadded only in an amount sufficient for compensating for leakage from thecasing 1. Therefore, a running cost can be reduced.

1. An apparatus for forming a desired gas atmosphere, comprising: acasing having a gas introduction opening for introducing a gas into thecasing and a gas discharge opening for discharging the gas from thecasing; a gas circulating tube passage fluidly communicated with thecasing for effecting circulation of the gas; a circulating fan foreffecting circulation of the gas in the casing through the gascirculating tube passage; and a valve switchable between a position forconducting the introducing and discharging of the gas into and from thecasing through the gas introduction opening and the gas dischargeopening and a position for effecting circulation of the gas in thecasing through the gas circulating tube passage.
 2. The apparatusaccording to claim 1, wherein the gas circulating tube passage isconnected between the gas introduction opening and the gas dischargeopening.
 3. The apparatus according to claim 2, wherein the switchablevalve comprises valves respectively provided at the gas introductionopening and the gas discharge opening.
 4. The apparatus according to anyone of claims 1 to 3, further comprising a particle-removing filter or achemical filter for removing particles contained in the circulated gas.5. The apparatus according to any one of claims 1 to 3, furthercomprising a trap provided in the gas circulating tube passage forcooling and condensing moisture contained in the gas passed through thecirculating tube passage and removing the moisture from the gas.
 6. Theapparatus according to claim 5, further comprising a heat exchanger foreffecting heat exchange between the gas which flows into the trap andthe gas which flows out of the trap.
 7. The apparatus according to claim3, further comprising: a filter for removing particles contained in thecirculated gas; a trap for cooling and condensing moisture contained inthe gas passed through the gas circulating tube passage and removing themoisture from the gas; and a heat exchanger for effecting heat exchangebetween the gas which flows into the trap and the gas which flows out ofthe trap.
 8. The apparatus according to claim 7, further comprising agas flow equalizing mechanism provided in the casing for equalizing flowof the gas passed through the casing.
 9. A method for forming a desiredgas atmosphere in a space in a casing, comprising the steps of:introducing a gas into the space while discharging the gas from thespace; and stopping the introducing and discharging of the gas when thespace is filled with the gas, and circulating the gas in the spacethrough a gas circulating passage communicated with the casing.
 10. Themethod according to claim 9, further comprising the step of conducting adesired treatment with respect to the circulated gas, such as removal ofparticles.
 11. The method according to claim 10, further comprising thestep of equalizing flow of the gas in the casing.
 12. The methodaccording to claim 9, wherein an inert gas is used as the gas.